Integrated circuit devices are widely used in consumer and commercial applications. As the integration density of integrated circuit devices continues to increase, it may be desirable to scale down features of integrated circuits such as electrode structures. As is well known to those having skill in the art, electrode structures may be used in integrated circuits for plate electrodes of a capacitor, for gate electrodes of a field effect transistor and/or for other uses.
For example, as silicon-based integrated circuit field effect transistors are scaled to below about 100 nm, it may be desirable to use dielectrics having high dielectric constants to obtain an equivalent oxide thickness below about 1 nm. Unfortunately, as equivalent oxide thickness continues to decrease, it may be undesirable to use polysilicon gate electrodes that are commonly used for integrated circuit field effect transistors, due, for example, to gate depletion and/or other potential problems.
It is also known that integrated circuit field effect transistors often are provided in complementary n-channel and p-channel devices. These n-channel devices often are referred to as NMOS devices and the p-channel devices often are referred to as PMOS devices. When supplied together on an integrated circuit, NMOS and PMOS devices are referred to as complementary MOS devices, or CMOS devices. It is known that it may be desirable for the work function of gate electrodes for NMOS devices to be about 4 eV, and for PMOS devices to be about 5 eV. Moreover, for processing purposes, it may be desirable to provide gate electrodes that can provide high thermal stability, so as to reduce or minimize undesirable changes under high temperature annealing.